1. Field of the Invention
The present invention relates to a multi-cylinder internal combustion engine, a vehicle, a marine vessel, and an exhausting method for a multi-cylinder internal combustion engine.
2. Description of the Related Art
Conventionally, in order to enhance the performance of internal combustion engines, gas exhaust devices of the internal combustion engines have been improved. For example, as described in Japanese Laid-Open Utility Model Publication No. 1-76520, an internal combustion engine including a convergent-divergent nozzle (generally called a “de Laval nozzle”) has been proposed in order to enhance the scavenging efficiency. The nozzle includes a convergent section including a flow path cross-sectional area which is decreased as a fluid progresses, a divergent section provided downstream with respect to the convergent section and including a flow path cross-sectional area which increases as the fluid progresses, and a throat section provided between the convergent section and the divergent section. When the pressure ratio of the pressure P0 in the convergent section and the pressure P in the divergent section (i.e., P/P0) is smaller than the critical pressure ratio (for the air, about 0.528), the velocity of the fluid exceeds the sonic velocity in the divergent section. Japanese Laid-Open Utility Model Publication No. 1-76520 has an object of improving the scavenging efficiency using this function of this nozzle. Specifically, as shown in FIG. 1 of Japanese Laid-Open Utility Model Publication No. 1-76520, six exhaust ports of the inline six-cylinder internal combustion engine are merged into a merging exhaust pipe. In addition, the exhaust path thereof is set to have such a length that increases the scavenging efficiency, and the nozzle is provided at the exhaust outlet of the merging exhaust pipe. Japanese Laid-Open Utility Model Publication No. 1-76520 describes that the exhaust gas flow, which has passed the nozzle and thus is increased in velocity, absorbs the exhaust gas remaining in the merging exhaust pipe, and thus the scavenging efficiency can be improved.